where \(\tau _{c}\)  is the mean collision time, \(k\)  is thermal conductivity and \(\tau \)  represents the relaxation time respectively [1]}[2]}.
The quantity \(\tau \)  measures the strength of relaxational effects and is called the causality index.
The values \(\tau =0\)  or \(\beta =0\)  represents the noncausal temperature profile.
<FIGURE>